1. Field of the Invention
The present invention relates to a method for increasing the flexibility and use of a telecommunications system. The invention relates further to a telecommunications system. The present invention relates also to an ATM board unit and a board rack arrangement for use in a telecommunications system.
2. Related Art and Other Considerations
A typical radio telecommunications system or Public Land Mobile Network (PLMN) comprises Base Stations (BS), Base Station Controllers (BSC) (which may also be referred to as Radio Network Controllers (RNC)) and Mobile Switching Centers (MSC). A BS is typically formed by one or several Base Transceiver Stations (BTS). The arrangement is such that the BTSs are capable of communicating with Mobile Stations (MS), such as mobile or cellular telephones, via a radio interface. A MSC is in turn arranged to provide an interface between the PLMN and an ordinary fixed network, such as a Public Switched Telephone Network (PSTN) or a Plain Old Telephone System (POTS). The PLMN thus comprises different kinds of nodes (MSCs, BSCs, etc.) arranged at appropriate positions in the network and capable of handling different kinds of information and providing different kinds of functionality to the network system, as will he described in more detail later.
Two common PLMN systems are based respectively on CDMA (Code Division Multiple Access) and TDMA (Time Division Multiple Access). For example, the IS-95 standard used in the USA is based on CDMA, whilst the widely used GSM standard (Global System for Mobile Communication) is based on TDMA. The principles of CDMA and TDMA are well known by the person skilled in the art of mobile communications, and are also specified by the international telecommunication organizations such as ITU-T (International Telecommunication Union-Telecommunication sector) and ETSI (European telecommunication Standard Institute), and are thus not explained in detail herein. It is sufficient to note that in CDMA systems different calls may be communicated using the same frequency but separated from each other by specific codes, whereas in TDMA systems the separation is accomplished by means of respective time slots reserved for each of the calls. The recent development of PLMNs is leading towards so called Wideband Cellular Systems (WCS) which are capable of supporting multimedia services, such as moving images and video. An example of a WCS is W-CDMA.
As mentioned above, in a PLMN, different kinds of information and/or operations are handled in different nodes thereof. A BSC node can be mentioned as one example, this node providing a large number of functions that need to be allocated to the available processing resources.
For example, present BSCs of cellular systems use pooled voice encoders/decoders (CODECs) for voice traffic. Each CODEC in the pool forms a resource which is handled and connected for a voice call when the need arises. Conventional systems have one CODEC allocated per Transceiver (TRX) or per user channel regardless of whether or not this is used. Data calls are also connected through the CODEC, although the function of the CODEC is passive in this case.